doc: In FDW handler docs, mark up scan_clauses with <literal>.

Etsuro Fujita

doc/src/sgml/fdwhandler.sgml

@@ -873,11 +873,11 @@ GetForeignServerByName(const char *name, bool missing_ok);
 
     <para>
      In <function>GetForeignPlan</>, generally the passed-in target list can
-     be copied into the plan node as-is.  The passed scan_clauses list
+     be copied into the plan node as-is.  The passed <literal>scan_clauses</> list
      contains the same clauses as <literal>baserel-&gt;baserestrictinfo</>,
      but may be re-ordered for better execution efficiency.  In simple cases
      the FDW can just strip <structname>RestrictInfo</> nodes from the
-     scan_clauses list (using <function>extract_actual_clauses</>) and put
+     <literal>scan_clauses</> list (using <function>extract_actual_clauses</>) and put
      all the clauses into the plan node's qual list, which means that all the
      clauses will be checked by the executor at run time.  More complex FDWs
      may be able to check some of the clauses internally, in which case those
@@ -895,7 +895,7 @@ GetForeignServerByName(const char *name, bool missing_ok);
      affect the cost estimate for the path.  The path's
      <structfield>fdw_private</> field would probably include a pointer to
      the identified clause's <structname>RestrictInfo</> node.  Then
-     <function>GetForeignPlan</> would remove that clause from scan_clauses,
+     <function>GetForeignPlan</> would remove that clause from <literal>scan_clauses</>,
      but add the <replaceable>sub_expression</> to <structfield>fdw_exprs</>
      to ensure that it gets massaged into executable form.  It would probably
      also put control information into the plan node's